Any form of thyroid disease – hypothyroidism, hyperthyroidism, or Hashimoto’s autoimmune thyroiditis – may adversely impact on a pregnancy. The pregnant state puts extra demands on the body, including thyroid function, as the baby develops. The thyroid is particularly affected during the first trimester, when the “pregnancy hormones” (hCG and estrogen) are high, tending to lower TSH. At the same time the fetus is completely dependent on the mother for thyroid hormones during the first trimester, moving to producing its own thyroid hormones only during the second trimester onwards.
For these reasons, anyone receiving thyroxine (T4) treatment, such as Synthroid, is likely to need an increase in dosage, to raise hormone levels in the body just as would happen naturally if the thyroid were fully-functioning.
What Happens If I Don’t Take Thyroxine During Pregnancy?
Untreated hypothyroidism always brings with it a raft of undesirable symptoms, including severe fatigue, “brain fog”, and depression. But hypothyroidism during pregnancy can lead to serious conditions for both mother and baby, including maternal anemia (low blood count), myopathy (muscle pain and weakness), pre-eclampsia (a hypertensive disorder), and even heart failure. For the baby, it may cause placental abnormalities, low birthweight, miscarriage or even stillbirth. Untreated severe hypothyroidism in the mother can also lead to impaired brain development in the baby.
The following findings would indicate possible hypothyroidism in the baby:
- Fetal tachycardia (fetal heart rate >160 bpm)
- Intrauterine growth restriction
- Fetal goiter
- Hydrops fetalis (a life-threatening condition of severe fluid-induced swelling).
How Much Thyroxine Should I Take During Pregnancy?
The treatment remains approximately the same, whether you are pregnant or not, except that the dosage of any thyroid medication is likely to need to be increased. Levothyroxine requirements may increase during pregnancy by 25–50 percent, or even double. Ideally you should optimize the dose before getting pregnant, have thyroid function levels tested immediately after getting pregnant, and re-test every 6-8 weeks during pregnancy. If you do need to change your levothyroxine dose, have your thyroid levels tested again four weeks later.
After you’ve had your baby, you will probably be able to return to a pre-pregnancy dosage. However, while Hashimoto’s autoimmune thyroiditis can improve during pregnancy, it often worsen after delivery, and symptoms of postpartum thyroiditis may be mistaken for “the baby blues”. Re-test your thyroid levels a few weeks after delivery to check how well your thyroid is adjusting.
Read more:
Risks to the Baby in a Hashimoto's Pregnancy
Why Isn't My Thyroxine Working?
References
- The American Thyroid Association, “Thyroid Disease and Pregnancy”, Patient Brochure 2008.
- “Transient Graves' hyperthyroidism during pregnancy in a patient with Hashimoto's hypothyroidism” Lu R, Burman KD, Jonklaas J.; Thyroid. 2005 Jul;15(7)..
- “Management of high-risk pregnancy”, Queenan & Spong, Wiley-Blackwell, 2007.
- Management of high-risk pregnancy”, Queenan & Spong, Wiley-Blackwell, 2007.
- “Autoimmune Thyroid Disease and Pregnancy”; Dotun A Ogunyemi, MD, Associate Professor of Obstetrics and Gynecology, David Geffen School of Medicine at UCLA; e.medicine 3 June 2009.
